HMDs, such as helmet-mounted displays and eyeglass-mounted displays, are display devices, worn on the head (e.g., as part of a helmet, eyeglasses, or visor) that has a display optic in front of one (monocular HMD) or both eyes (binocular HMD). As further described below, an HMD typically includes optical displays with lenses and semi-transparent mirrors. The displays are generally miniaturized and may include light emitting diodes (LEDs), liquid crystal displays (LCDs), etc.
HMDs differ from one another in several aspects. For example, some HMDs can only display a computer-generated image (CGI), which may be referred to as a virtual image. Other HMDs are able to show a combination of a CGI and live images from the real world. Such embodiments can be referred to as augmented reality.
Although HMDs have been developed for use in numerous applications (e.g., gaming, medicine, training/simulation), continued use often causes the user's eyesight to be strained. Extended exposure to virtual and augmented reality environments has also been associated with symptoms similar to motion sickness, such as general discomfort, headache, nausea, and disorientation. Therefore, a need exists to improve the general effectiveness of HMDs and the comfort of users, especially those who are exposed to virtual or augmented reality for extended periods of time.